1. Field of the Invention
The present invention relates to methods and apparatus for forming images including the steps of visualizing electrostatic latent images or magnetic images with developer and recording the visualized images on a recording material by microwave fixing. The steps are carried out in accordance with a known image forming method such as an electrophotographic process an, electrostatic recording process or a magnetic recording process. The term "microwave" as used herein is to be understood to mean those electromagnetic waves whose wavelength is less than several meters and to include also sub-millimeter region waves having wavelength less than 1 mm close to the far infrared region.
2. Description of the Prior Art
A copying apparatus provided with a microwave dielectric heating fixing system is already known in the art. In this type of copying machines microwaves are used for fixing. This has a particular advantage that a wait time is no longer required to warm up fixing rollers and other members, and further there is no problem of offset. The microwave dielectric heating fixing method according to the prior art uses a dielectric material that is able to absorb and generate heat. Such dielectric material is admixed with thermoplastic developer in order to make full use of microwave radiation. The dielectric developer is introduced into a high frequency electric field to induce a polarization oscillation within the dielectric material thereby transforming microwave radiation into thermal energy. The thermal energy melts the main component resin of the developer, a thermoplastic resin, whereby the developed image is fixed on the recording material.
As will be understood from the above, if there is used, as the dielectric material in the developer or in the developed image, such material which has a higher microwave dielectric loss, then a substantial improvement in microwave absorption and therefore a substantial improvement in fixability can be attained.
However, until now, a suitable resin has not been available which can satisfy the requirements of high dielectric loss and low melting point at the same time. For this reason, a mixture of two different materials has been used as the developer for microwave fixing. The mixture contains material of high dielectric loss and material of low melting point.
Resin having higher dielectric loss is more exothermic. In the mixture, the heat generated from the resin of high dielectric loss by microwave is transmitted to another component resin of low melting point through surface-surface contact of the two materials. Use of a high content of the resin of high dielectric loss is limited by the heat transmission time. If the content is high, the heat transmission time becomes long. Therefore, it is very difficult to obtain a developer which exhibits good fixativeness in a short time. There has not been developed yet any developer having satisfactory thermal efficiency.
As another attempt to improve the fixativeness of such developer, the amount of microwave radiation has been increased. But, this attempt has resulted in failure. Increase of microwave output has increased only the quantity of wasted microwave radiation. The increased microwave radiation was used in vain.
The most important problem in microwave heating fixing system is, therefore, how to efficiently convert microwave radiation into fixing energy. Now, there is an increasing demand for a novel technique by which the fixativeness and fixing speed can be improved.